library(maptools)
library(rgdal)
# Download and extract grids:
download.file("http://spatial-analyst.net/book/system/files/usgrids5km.zip", destfile=paste(getwd(), "usgrids5km.zip", sep="/"))
grid.list <- c("dairp.asc", "dmino.asc", "dquksig.asc", "dTRI.asc", "gcarb.asc", "geomap.asc", "globedem.asc", 
"minotype.asc", "nlights03.asc", "sdroads.asc", "twi.asc", "vsky.asc", "winde.asc", "glwd31.asc")
for(j in grid.list){
fname <- zip.file.extract(file=j, zipname="usgrids5km.zip")
file.copy(fname, paste("./", j, sep=""), overwrite=TRUE)
}
# plot the predictors:
library(adehabitat)
image(as.kasc(list(geomap=import.asc("geomap.asc"), nlights03=import.asc("nlights03.asc"), 
dTRI=import.asc("dTRI.asc"), gcarb=import.asc("gcarb.asc"))))